This invention relates to telecommunication systems that can simultaneously support plain old telephone services (POTS) including on-hook transmission, digital subscriber line services (XDSL) and periodic pulse metering (PPM) signals. The invention is especially suited but not limited to allocating overhead voltage for these signals.
Telephone networks use batteries of approximately 48 to 52 Volts (V) of direct current (DC), located at a central office, to drive customer premises equipment (CPE), such as a standard telephone, at a customer premises. In a POTS mode of operation, a normal office battery voltage is acceptable because a standard CPE device typically needs at least between 16 to 22 milliamps (mA) of DC current to operate. The impedance of the telephone loop (path between the central office and the CPE) typically changes based on the loop configurations. When POTS, XDSL and PPM signals are transmitted simultaneously, the combination of corresponding overhead voltages along with the needed DC voltage are not fully supported by the output of the battery on some loop configurations. This results in either lowering the maximum data rates of the XDSL due to reduced signal levels, reducing PPM signal levels, reducing the voice quality (level) of the POTS signal, or a combination thereof.
Attempts at solving this problem have included using higher voltage batteries, separate drive circuits for these signals, and battery boost circuits. However, each of these solutions has included expensive new circuitry and the associated software to control it. Therefore, there is a need for a system and method for allocating overhead voltage to allow the transmission of POTS including on-hook transmission, XDSL and PPM signals either separately or simultaneously. There is a need to support such simultaneous signals in the United States and around the world with standard central office batteries with standard maximum available voltage.